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Structure

The compound has a dimeric structure that is centrosymmetric. Each allyl group lies in a plane at an angle of about 111.5° to the square formed by the palladium and carbon atoms, and the Pd–C distances are all equal. Its unit cell is monoclinic.²

Synthesis

The compound is prepared by purging carbon monoxide through a methanolic aqueous solution of sodium tetrachloropalladate (prepared from palladium(II) chloride and sodium chloride), and allyl chloride.³

2 Na2PdCl4   +   2 CH2=CHCH2Cl   +   2 CO   +   2 H2O   →   [(η3-C3H5)PdCl]2   +   4 NaCl   +   2 CO2   +   4 HCl

Another method is the reaction of propene with palladium(II) trifluoroacetate, followed by ion exchange with chloride:⁴

2 (CF3COO)2Pd + 2 CH2=CHCH3 → [(η3-C3H5)Pd(CF3COO)]2 [(η3-C3H5)Pd(CF3COO)]2 + 2 Cl− → [(η3-C3H5)PdCl]2 + 2 CF3COO−

Reactions

APC reacts with sources of cyclopentadienyl anion to give the corresponding 18e− complex cyclopentadienyl allyl palladium:

[(η3-C3H5)PdCl]2   +   2 NaC5H5   →   2 [(η5-C5H5)Pd(η3-C3H5)]   +   2 NaCl

The dimer reacts with a variety of Lewis bases (:B) to form adducts (η3-C3H5)PdCl:B. Its reaction with pyridine and the corresponding enthalpy are:

1/2 [(η3-C3H5)PdCl]2 + :NC5H5 → (η3-C3H5)PdCl:NC5H5 ΔH=−30.1 kJ.mol−1

This enthalpy corresponds to the enthalpy change for a reaction forming one mole of the product, (η3-C3H5)PdCl:NC5H5, from the acid dimer. The dissociation energy for the Pd dimer, which is an energy contribution prior to reaction with the donor,

[(η3-C3H5)PdCl]2 → 2 (η3-C3H5)PdCl

has been determined by the ECW model to be 28 kJ.mol−1.

APC catalyzes many organic reactions, such as cross-coupling, nucleophilic addition to dienes, and decomposition of diazo compounds to reactive carbenes. It is also a useful precursor of other Pd catalysts.⁵

References

1. Tatsuno, Y.; Yoshida, T.; Otsuka, S. "(η3-allyl)palladium(II) Complexes" Inorganic Syntheses, 1990, volume 28, pages 342-345. ISBN 0-471-52619-3 /wiki/Inorganic_Syntheses ↩

2. Smith, A. E. (1965). "The structure of the allylpalladium chloride complex (C3H5PdCl)2 at –140°C". Acta Crystallographica. 18 (3): 331–340. Bibcode:1965AcCry..18..331S. doi:10.1107/S0365110X65000774. ISSN 0365-110X. http://scripts.iucr.org/cgi-bin/paper?S0365110X65000774 ↩

3. Tatsuno, Y.; Yoshida, T.; Otsuka, S. "(η3-allyl)palladium(II) Complexes" Inorganic Syntheses, 1990, volume 28, pages 342-345. ISBN 0-471-52619-3 /wiki/Inorganic_Syntheses ↩

4. Godleski, Stephen A.; Michelet, Véronique; Genêt, Jean-Pierre (2006), "Bis(allyl)di-μ-chlorodipalladium", Encyclopedia of Reagents for Organic Synthesis, Chichester, UK: John Wiley & Sons, Ltd, doi:10.1002/047084289x.rb098s.pub2, ISBN 978-0-471-93623-7, retrieved 2020-09-06 978-0-471-93623-7 ↩

5. Godleski, Stephen A.; Michelet, Véronique; Genêt, Jean-Pierre (2006), "Bis(allyl)di-μ-chlorodipalladium", Encyclopedia of Reagents for Organic Synthesis, Chichester, UK: John Wiley & Sons, Ltd, doi:10.1002/047084289x.rb098s.pub2, ISBN 978-0-471-93623-7, retrieved 2020-09-06 978-0-471-93623-7 ↩